Duplicate emails with Email Security.cloud

Products

• Email Security.cloud

Issue/Introduction

You are seeing duplicate copies of email being delivered to one of your users or a third-party reports receiving duplicates of emails from your user.

Resolution

The table below lists the most likely reasons that may cause duplicate emails. 

Once you have established the nature of the problem, we can investigate if the duplication is occurring within our infrastructure.

 

Cause	Description	Troubleshooting
The email server is overloaded	If your email server is overloaded, you may need to set a limit to the amount of concurrent connections that the server accepts. If the email server response is slow. Connections requests are sent until the email server replies. If the server is set to do reverse DNS lookups before performing security checks, MessageLabs keeps sending the email again If the message size limits is set too low, the email server can either take too long to respond or it has reached its limit. In both cases, MessageLabs resends the email. You are subjected to a DOS/SPAM attack. A DOS/SPAM attack takes up all of your bandwidth, resulting in the inability to receive	Check the available bandwidth, the email server capability and the number of connections to accept (50 is usually an acceptable number of connections.)
Out of date CISCO PIX firewall	It is a known issue. The CISCO software resets the connection if the "." and the email ending are in two different TCP packets. The wildcard and the email ending in separate TCP packets does not match MessageLabs expected protocol  In this instance, MessageLabs resends the email.	Solution 1: Upgrade the PIX software Solution 2: Disable the SMTP fixup protocol in the CISCO PIX configuration so that our email servers can send emails to your email server instead of PIX acting as an intermediate relay. Visit CISCO and search for CISCO defect number CSCds90792.    A patch exists for the PIX software, versions 5.2.4 and 5.2.5. For newer PIX versions, we recommend that you disable "ESMTP Inspect".
POP issues	A POP server sets the email status to "downloaded" after emails have been downloaded. If the email retrieving process is interrupted, the email client restart downloading emails from the beginning	Check connectivity
Setup issues	The server is not set up to delete emails from the server after download	Check your server settings and ensure that it is set to delete emails after they have been downloaded.
Multiple sending	The sender has sent an email multiple times	Select two duplicate emails randomly and check their message IDs